‘It was implicit in the terms of sections 73 and 73A of the Town and Country Planning Act 1990, as amended, that in an appropriate case a planning authority considering an application under section 73 for planning permission to proceed with a development without complying with conditions attached to an existing permission might grant, under section 73A, retrospective planning permission for a development already carried out, subject to conditions imposed under section 70. There might be some unusual circumstance that would require the inspector to forewarn the applicant that he was minded to act under section 73A.’